Some networks have a centralized controller that provides scheduled point-to-point communications, and may also coordinate a contention channel. These networks may also allow point-to-multipoint communication links between devices, but only of limited capacity. These types of networks will be referred to as centralized networks. In contrast, networks that have a shared medium, such as those having a broadcast channel, or those that have no centralized controller, such as Internet Protocol (IP) networks or other distributed networks operating by an agreed-upon standard.
In centralized networks, communications between devices are generally scheduled and controlled by the central controller. If device A needs to send something to device B, device A must either send the communication to the central controller, which then sends it to device B, or device A must send a message to the central controller indicating the desire to send something to device B. In the latter example, the central controller then notifies all of the devices on the network to stay off the network at a certain point in time, as device A will be allowed to send the communication to device B at that time. Some systems may support a contention access channel, a first-come-first-served channel access for which the devices contend.
Because of the point-to-point nature of these systems, as well as the need for a centralized controller, there are no current methods to allow for broadcast or multicast messages in these systems. A broadcast message is one sent to all devices on the network, while a multicast system is one sent to a specified subset of the network. Centralized networks may have the ability to send point-to-multipoint messages, which are in essence a multicast message, but the capabilities are limited.